DESCRIPTION: The long-term objective of this research program is to understand how the auditory system processes information in rooms with echoes. The experiments will focus on the precedence effect which describes aspects of competition for perception and localization between a sound source and its echoes. Proposed studies will systematically explore several perceptual phenomena that are involved in precedence and results will be interpreted in the context of a descriptive model of precedence. These studies will be conducted in parallel with the P.I.'s work on neural correlates of precedence in the auditory brainstem. Aim 1 investigates the importance of the relative locations in a room of the source (lead) and echo (lag). This is a significant question since precedence is generally assumed to play an important role in directional hearing, however, little empirical data are available to support this assumption. Aim 2 is to validate the use of virtual-acoustic-space (VAS) stimuli for precedence studies so that all directional cues can be brought under tight experimental control, allowing manipulation of the relative directional information provided to the two ears. Aim 3 is to measure precedence in free field and using VAS stimuli in the azimuthal plane (where binaural disparity cues dominate localization) and in the median-sagittal plane (where spectral cues dominate localization). These studies test fundamental hypotheses concerning the extent to which monaural and binaural mechanisms mediate precedence. Aim 4 extends investigations of precedence to a multiple-echo paradigm, thus bringing these studies closer to a realistic environment which normally contains a complex array of echoes. To date, very little research on this topic has been done. This work may help clarify why listeners with hearing impairments have difficulty extracting important information in the presence of reverberations and competing sounds, and may help develop hearing aids geared towards eliminating interference in reverberant environments.